The blood composition of Friesian bulls; variations with age and relationships with results of progeny tests

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Abstract
Summary: Blood samples were taken from 172 Friesian bulls during 1973–5 on three or four occasions. The bulls were in Milk Marketing Board cattle breeding centres in England and Wales and were from 1 to 14 years of age.The blood samples were analysed for packed cell volume, haemoglobin, erythrocytes, mean corpuscular volume and glucose, and samples of serum for the concentrations of albumin, total protein, urea-nitrogen, inorganic phosphate, Ca, Mg, K, Na and Cu.Packed cell volumes and haemoglobin and K concentrations were higher in bulls than those previously recorded in dairy cows. There were significant age relationships for packed cell volume, haemoglobin, albumin and globulin (P < 0·001), inorganic phosphate and erythrocytes (P < 0·01) and Ca and Mg (P < 0·05).Repeatability estimates were calculated and compared with estimates previously obtained for dairy cows.On the basis of improved contemporary comparisons of the bulls, there was a significant relationship between the average milk yield of a bulls daughters and the concentrations of urea, inorganic phosphate and K (P < 0·05) in the blood serum of the bull.